1. Field of the invention
This invention relates to molded calcium silicate articles having a superior workability and a method for producing the same.
More particularly, this invention relates to molded calcium silicate articles comprising hydrated calcium silicate and powdered resin, which have an advantageous combination of properties of light weight high refractoriness and good dimensional stability together with a workability comparable with or better than wooden materials and which are suitable as materials for the fabrication of various molds, models and structural components used in art and industrial applications and can be subjected to processing operations while greatly reducing the amount of generated dust. This invention is also directed to a method for the production of such useful molded calcium silicate articles.
2. Description of the Prior Art
Hydrated calcium silicate is sold as various molded articles because of its advantageous properties of light weight and thermal stability. Particularly, attempts have been made to produce artificial wood-like materials by molding hydrated calcium silicate having a bulk density of 0.3 to 0.7 g/cm.sup.3. There may be mentioned the following molded calcium silicate articles.
(1) Molded calcium silicate prepared by molding an aqueous slurry consisting of 100 parts by weight of hydrated calcium silicate, 10 to 150 parts by weight of hydraulic gypsum, 5 to 30 parts by weight of a polymer emulsion, a coagulating agent for the polymer emulsion, water and reinforcing fiber, and drying the resultant molded body (Japanese Patent Application Laid-Open No. 54-160 428)
(2) Molded calcium silicate prepared by molding an aqueous slurry consisting of 100 parts by weight of hydrated calcium silicate and 5 to 30 parts by weight (as solid content) of a latex of styrene-butadiene copolymer having carboxyl groups, a cationic high molecular weight coagulant and water, and drying the resultant molded bodies (Japanese Patent Application Laid-Open No. 60 - 246 251)
Further, in order to improve the disadvantages of the above prior inventions, the present applicant has proposed the following calcium silicate molded articles.
(3) Molded calcium silicate consisting of 100 parts by weight of hydrated calcium silicate, 1 to 30 parts by weight of a reinforcing fiber, 1 to 40 parts by weight of a latex and 0.1 to 5 parts by weight of a dispersant (Japanese Patent Application Laid-Open No. 62 - 123 053)
(4) Molded calcium silicate prepared by adding a substance capable of forming ettringite by reaction with water in an amount of 1 to 15 parts by weight relative to 100 parts by weight of hydrated calcium silicate, into the composition of the molded calcium silicate proposed in (3) (Japanese Patent Application Laid-Open No. 62 - 235 276)
However, since the molded calcium silicate set forth in (1) has an insufficient bending strength, at most about 100 kgf/cm.sup.2, and includes a large amount of hydraulic gypsum, the molded calcium silicate articles will present problems in machinability, dusting characteristics, thermal resistance and dimensional stability, when it is subjected to processing operations.
The molded calcium silicate articles mentioned above in (2), (3) and (4) were developed especially with the object of improving thermal resistance and strength among the physical properties as mentioned in the molded calcium silicate (1), and almost no attention has been paid to the problems of machinability and dust produced during machining operations.